A modular gas level measuring device in a liquefied gas tank includes a plurality of modular float assemblies releasably connecting together. Each of the plurality of modular float assemblies includes a float. A sensing assembly releasably connects with the plurality of modular float assemblies and includes a biasing member subject to weights of the plurality of modular float assemblies and with an original length. The biasing member deforms from the original length thereof and has various deformed lengths with respect to displacements of the plurality of modular float assemblies.